1. Field of the Invention
The present invention pertains to the field of devices that reduce the transmission of radiation, and particularly to devices that reduce the transmission of infrared light.
2. Description of the Related Art
Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Glass laminated products or safety glass have contributed to society for almost a century. Safety glass is characterized by high impact and penetration resistance, and by minimal scattering of glass shards and debris upon shattering. The laminates typically consist of a sandwich of an interlayer that is a polymeric film or sheet, and that is placed between two glass sheets or panels. One or both of the glass sheets may be replaced with optically clear rigid or non-rigid polymeric sheets such as, for example, sheets of polycarbonate materials or polyester films. Safety glass has further evolved to include more than two layers of glass and/or polymeric sheets bonded together with more than one interlayer.
The interlayer is typically made with a relatively thick polymer film or sheet that exhibits toughness and adheres to the glass in the event of a crack or crash. Over the years, a wide variety of polymeric interlayers have been developed for glass laminated products. In general, it is desirable that these polymeric interlayers possess acceptable levels of: optical clarity, impact resistance, penetration resistance, ultraviolet light resistance, long term thermal stability, adhesion to glass and/or other rigid polymeric sheets, ultraviolet light transmittance, moisture absorption, moisture resistance, long term weatherability, and haze of less than 4%, among other characteristics.
Widely used interlayer materials include complex multi-component compositions comprising polymers such as: polyvinylbutyral (PVB), polyurethane (PU), polyvinylchloride (PVC), metallocene-catalyzed linear low density polyethylenes (mPE), ethylenevinyl acetate (EVA), ethylene acid copolymer ionomers, polymeric fatty acid polyamides, polyester resins such as poly(ethylene terephthalate) (PET), silicone elastomers, epoxy resins, and elastomeric polycarbonates. The use of acid copolymers in fabricating transparent laminates has become more widespread.
Beyond the well known safety glass commonly used in automotive windshields, glass laminates are incorporated as windows into trains, airplanes, ships, and nearly every other mode of transportation. The architectural use of safety glass has also expanded rapidly in recent years, as designers incorporate more glass surfaces into buildings. In addition to their desirable aesthetic features, glass laminated products have now attained the strength required for weight bearing structures such as, for example, the glass staircases and balustrades featured in many newer buildings.
The newer safety glass products are also designed to resist natural and man made disasters. Examples include the recent development of the hurricane resistant glass that is now mandated in many hurricane susceptible areas, theft resistant glazings, and blast resistant glass laminated products. These products have enough strength to resist intrusion even after the frangible portion of the laminate has been broken, for example by high force winds, or by impact of flying debris, or by a criminal attempting to break into a building or vehicle.
Society continues to demand more functionality from laminated glass products beyond its optical and decorative capabilities and the safety characteristics described above. One desirable goal is the reduction of energy consumption within structures, such as automobiles or buildings, for example, through the development of solar control glazing. Because the near infrared spectrum is not sensed by the human eye, a typical approach has been to develop glass laminates that prevent a portion of solar energy from the near infrared spectrum from entering the structure. For example, the energy expended on air conditioning may be reduced, without a reduction or distortion of the transmitted visible light spectrum, in structures equipped with solar control windows that block a portion of the near infrared spectrum.
Solar control in glass laminates may be achieved through modification of the glass or of the polymeric interlayer, by the addition of further solar control layers, or combinations of these approaches. One form of solar control laminated glass includes metallized substrate films, such as polyester films, which have electrically conductive metal layers, such as aluminum or silver metal. The metallized films generally reflect light of the appropriate wavelengths to provide adequate solar control properties. Metallized films, however, are commonly manufactured by vacuum deposition or sputtering processes that require a high vacuum apparatus and a precision atmosphere controlling system.
In addition to infrared light, metallized films also reflect certain radio wavelengths, thus impairing the function of radio, television, global positioning systems (GPS), automated toll collection, keyless entry, communication systems, automatic garage openers, automated teller machines, radio frequency identification (RFID), and like systems commonly used in automobiles or other structures that may be protected by solar control laminated glass. This impairment is a direct result of the metal layers being continuous and, therefore, electrically conductive.
Finally, moisture intrusion into sputtered metal coated films during and after the glass lamination process requires additional, complicated processes to allow for edge deletions from the interlayer. To overcome these problems and others, metallized films have been used as inner layers in laminated glass structures. This type of structure complicates the manufacturing processes.
A more recent trend has been the use of metal oxide nanoparticles that absorb rather than reflect infrared light. To preserve the clarity and transparency of the substrate, these materials ideally have nominal particle sizes below about 200 nanometers (nm). Because these materials do not form electrically conductive films, the operation of radiation transmitting and receiving equipment located inside structures protected by this type of solar control glazing is not impeded.
Two infrared absorbing metal oxides that have attained commercial significance are indium tin oxide and antimony tin oxide. Several film substrates coated with antimony tin oxide and/or indium tin oxide have been described as solar control window coverings. See, for example, U.S. Pat. No. 5,518,810. The metal oxide particles may be adhered to windows as a window covering with a thin layer of contact adhesive. See, for example, U.S. Pat. Nos. 6,191,884; 6,261,684 and 6,528,156.
Lanthanum hexaboride is another example of an infrared absorbing inorganic compound that has attained commercial significance. Lanthanum hexaboride is reported to be more efficient than other inorganic infrared absorbing nanoparticles, such as antimony tin oxide and indium tin oxide, for example. Therefore, equivalent solar control performance may be obtained at a relatively low level of nanoparticles.
Several film substrates coated with lanthanum hexaboride have been described as solar control window coverings. See, for example, U.S. Pat. Nos. 6,060,154; 6,221,945; 6,277,187; and 6,319,613; and
European Patent No. 1 008 564. Moreover, lanthanum hexaboride has been used in combination with antimony tin oxide and indium tin oxide in a hardcoat layer of a window covering. See, for example, U.S. Pat. No. 6,663,950.
Window coverings, however, suffer the shortcomings of being unstable to aging and environmental stresses such as cleaning. Over time they may develop scratches or stress cracks on the film. They may also form bubbles or otherwise develop partial or total lack of adhesion to the window from, for example, humidity, heat or both.
Therefore, nanoparticles have been incorporated into the polymeric interlayers of glass laminates. Generally, the nanoparticles are introduced into the polymeric materials as a dispersion in a vehicle such as a plasticizer, a solvent, or another liquid. Alternatively, ultrafine metal oxide particles have been introduced directly into a polymer melt at the end concentration desired for the infrared absorbing interlayer. See, for example, U.S. Pat. Nos. 5,830,568; 6,315,848; 6,329,061; 6,579,608; 6,506,487; 6,620,477; 6,686,032; 6,632,274; 6,673,456; and 6,733,872; U.S. Appin. Pubin. Nos. 2004/0071957; 2004/0131845; and 2004/0028920 and Internatl. Appln. Publn. No. WO 02/060988. The addition of the nanoparticles into the polymeric interlayers necessarily complicates the processes by which these laminates are produced.
It remains desirable to provide new devices that reduce transmission of infrared energy without impeding radio frequency transmission.